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2004 Kawasaki KX250 wont start just backfires

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Hi all,

I have a 2004 kx 250 2 stroke and it wont start.  it only backfires.  I was out riding it one day and came up to a stop so the bike was just idling and it started to try and die so i revved it up a few times then let it die and now it wont start back up.  It only pops or backfires when you kick it.  Its getting good spark and i just put a brand new plug and coil in it. I took the reeds apart and they look like they're brand new.  It was running great before so i dont know what happened.  Im thinking it could be a fuel problem even tho the plug is a little wet if you take it out after a bunch of kicking.  Any help would be greatly appreciated 

 

Thanks

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how long been sitting? If your last fuel fill up was with pump gas containing up to 10% ethanol and it has sat over the winter there is likely green goo inside the float bowl and plugging the pilot jet. Clean it all off and buy a new pilot jet. Don't let pump gas sit for over 30 days ever.

Edited by shrubitup

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how long been sitting? If your last fuel fill up was with pump gas containing up to 10% ethanol and it has sat over the winter there is likely green goo inside the float bowl and plugging the pilot jet. Clean it all off and buy a new pilot jet. Don't let pump gas sit for over 30 days ever.

It had been sitting for about a day. Fresh 32:1 gas in it and when I got it out I started 1st kick. I let it warm up for a little bit and took off. It ran great for about 10 min then it died. Carb has been completely rebuilt

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Check that your woodruff key hasn't sheared off. It's what aligns your flywheel on the crank so that your ignition timing is correct.

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I’ll backup SS109 and tell you to check your Woodruff Key. I have seen this problem before with many a KX250.

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I had the woodroof key issue on a stihl 046, after I packed it deep in to the forest. 

While you are in there, check the timing marks. 

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Check that your woodruff key hasn't sheared off. It's what aligns your flywheel on the crank so that your ignition timing is correct.

Key is intact
I had the woodroof key issue on a stihl 046, after I packed it deep in to the forest. 
While you are in there, check the timing marks. 

Key is intact
I’ll backup SS109 and tell you to check your Woodruff Key. I have seen this problem before with many a KX250.

Key is intact

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This will sound even more dumb, but make sure your spark cap is snapping in to place.  I had an issue recently where the screw on plug terminal stripped/unscrewed and came off in the cap.  When I went to reinstall it would not wasn't making the best connection, and I wondered why the bike suddenly had a spark plug terminal similar to a briggs and stratton.

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This will sound even more dumb, but make sure your spark cap is snapping in to place.  I had an issue recently where the screw on plug terminal stripped/unscrewed and came off in the cap.  When I went to reinstall it would not wasn't making the best connection, and I wondered why the bike suddenly had a spark plug terminal similar to a briggs and stratton.

Coil and cap is all new

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35 minutes ago, luke8500 said:


Coil and cap is all new

That is even more reason for them to be suspect.

The carb being "completely rebuilt" also makes it suspect.  Did your "complete rebuild" include a jet block gasket?  Did the "complete" rebuild mean that you are certain that the jets are fully seated?  

Did you confirm the float is working correctly?

Did you confirm the setting of the air screw?

Do you own a manual?

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Big end bearing on crank took a crap possibly 😕

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Big end bearing on crank took a crap possibly

I don’t see how that could cause its problem

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Just now, luke8500 said:


I don’t see how that could cause its problem

That's what they do when go but ok . does it feel funny kicking over by hand? Can you pour little gas in cyl will it start? Not saying that's your problem but those are symptoms of crank toasted 

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That is even more reason for them to be suspect.
The carb being "completely rebuilt" also makes it suspect.  Did your "complete rebuild" include a jet block gasket?  Did the "complete" rebuild mean that you are certain that the jets are fully seated?  
Did you confirm the float is working correctly?
Did you confirm the setting of the air screw?
Do you own a manual?

Yes everything’s good in the carb. Ran great with the rebuild carb for awhile then this happened
That's what they do when go but ok . does it feel funny kicking over by hand? Can you pour little gas in cyl will it start? Not saying that's your problem but those are symptoms of crank toasted 

Motor feels normal when kicking. I did get it to start but it sounded like a 4 stroke and would only start if I held the throttle wide open while kicking

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I am kind leaning towards what 367 said.  I just lost a big end a few months ago, and the same clues apply, with the addition hearing more noise right before it stopped running. 

 

If you still have the flywheel cover off, check for slop in the c-rod. 

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I am kind leaning towards what 367 said.  I just lost a big end a few months ago, and the same clues apply, with the addition hearing more noise right before it stopped running. 
 
If you still have the flywheel cover off, check for slop in the c-rod. 

Bearings feels tight. Spun motor over with no plug in it and it didn’t make any unusual sounds.

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UPDATE- booking a timing light to it and turned the motor over really fast and it is sparking really late. I’m thinking stator or cdi

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UPDATE- booking a timing light to it and turned the motor over really fast and it is sparking really late. I’m thinking stator or cdi


Either one of those should be it! Good luck.

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